1. Technical Field
The present invention relates to a tunable optical device, and more particularly to an optical interleaver/deinterleaver including an array of micro-mirrors to optically separate a WDM signal into subsets of optical channels or combine a pair of WDM signals comprising subsets of spaced optical channels.
2. Description of Related Art
FIG. 1 shows a known interleaver device that combines at least two optical WDM input signals 2,3 into a single optical output signal 4. The WDM input signals include a plurality of wavelength bands of light (or optical channels) that are centered at a respective channel wavelength (λ1, λ2, λ3, . . . λN). In one embodiment, as shown, one input signal 2 includes each even input channel 14 (e.g., λ2, λ4, λ6), and the other input signal 3 includes each odd input channel (e.g., λ1, λ3, λ5). The combined input signals 2,3 provide a WDM output signal having each input channels 14,14′ (e.g., λ1-λ6).
FIG. 2 shows another known optical deinterleaver device generally indicated as 5 that separates an optical WDM input signal 6 into at least two optical output signals 7, 8. The WDM input signal includes a plurality of optical channels that are centered at a respective channel wavelength (λ1, λ2, λ3, . . . λN). In one embodiment, as shown, the input signal 6 includes a WDM output signal having input channels at λ1-λ6. The input signal 6 is separated such that one output signal 7 includes each even input channel (i.e., λ2, λ4, λ6), and the other output signal 8 includes each odd input channel (i.e., λ1, λ3, λ5).
Moreover, MEMS micro-mirrors have been widely explored and used for optical switching applications. The most commonly used application is for optical cross-connect switching. In most cases, individual micro-mirror elements are used to ‘steer’ a beam (i.e., an optical channel) to a switched port or to deflect the beam to provide attenuation on a channel-by-channel basis. Each system is designed for a particular ‘wavelength plan’—e.g. “X” number of channels at a spacing “Y”, and therefore each system is not ‘scalable’ to other wavelength plans.
In the networking systems, it is often necessary to route different channels (i.e., wavelengths) between one fiber and another using a reconfigurable optical add/drop multiplexer (OADM) and/or an optical cross-connect device. Many technologies can be used to accomplish this purpose, such as Bragg gratings or other wavelength selective filters.
One disadvantage of Bragg grating technology is that it requires many discrete gratings and/or switches, which makes a 40 or 80 channel device quite expensive.
A better alternative would be to use techniques well-known in spectroscopy to spatially separate different wavelengths or channels using bulk diffraction grating technology. For example, each channel of an interleaver device is provided to a different location on a generic micro-electro-mechanical system (MEMS) device. The MEMS device is composed of a series of tilting mirrors, where each discrete channel hits near the center of a respective mirror and does not hit the edges. In other words, one optical channel reflects off a single respective mirror.
One issue with the above optical MEMS device is that it is not “channel plan independent”. In other words, each MEMS device is limited to the channel spacing (or channel plan) originally provide. Another concern is that if the absolute value of a channel wavelength changes, a respective optical signal may begin to hit an edge of a corresponding mirror leading to large diffraction losses. Further, since each channel is aligned to an individual mirror, the device must be carefully adjusted during manufacturing and kept in alignment when operated through its full temperature range in the field.
It would be advantageous to provide an optical interleaver/deinterleaver that mitigates the above problems by using an array of micro-mirrors.